/src/libjpeg-turbo.main/src/jdpostct.c

Source
/*
 * jdpostct.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1994-1996, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2022-2024, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains the decompression postprocessing controller.
 * This controller manages the upsampling, color conversion, and color
 * quantization/reduction steps; specifically, it controls the buffering
 * between upsample/color conversion and color quantization/reduction.
 *
 * If no color quantization/reduction is required, then this module has no
 * work to do, and it just hands off to the upsample/color conversion code.
 * An integrated upsample/convert/quantize process would replace this module
 * entirely.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jsamplecomp.h"


#if BITS_IN_JSAMPLE != 16 || defined(D_LOSSLESS_SUPPORTED)

/* Private buffer controller object */

typedef struct {
  struct jpeg_d_post_controller pub; /* public fields */

  /* Color quantization source buffer: this holds output data from
   * the upsample/color conversion step to be passed to the quantizer.
   * For two-pass color quantization, we need a full-image buffer;
   * for one-pass operation, a strip buffer is sufficient.
   */
  jvirt_sarray_ptr whole_image; /* virtual array, or NULL if one-pass */
  _JSAMPARRAY buffer;           /* strip buffer, or current strip of virtual */
  JDIMENSION strip_height;      /* buffer size in rows */
  /* for two-pass mode only: */
  JDIMENSION starting_row;      /* row # of first row in current strip */
  JDIMENSION next_row;          /* index of next row to fill/empty in strip */
} my_post_controller;

typedef my_post_controller *my_post_ptr;


/* Forward declarations */
#if BITS_IN_JSAMPLE != 16
METHODDEF(void) post_process_1pass(j_decompress_ptr cinfo,
                                   _JSAMPIMAGE input_buf,
                                   JDIMENSION *in_row_group_ctr,
                                   JDIMENSION in_row_groups_avail,
                                   _JSAMPARRAY output_buf,
                                   JDIMENSION *out_row_ctr,
                                   JDIMENSION out_rows_avail);
#endif
#if defined(QUANT_2PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16
METHODDEF(void) post_process_prepass(j_decompress_ptr cinfo,
                                     _JSAMPIMAGE input_buf,
                                     JDIMENSION *in_row_group_ctr,
                                     JDIMENSION in_row_groups_avail,
                                     _JSAMPARRAY output_buf,
                                     JDIMENSION *out_row_ctr,
                                     JDIMENSION out_rows_avail);
METHODDEF(void) post_process_2pass(j_decompress_ptr cinfo,
                                   _JSAMPIMAGE input_buf,
                                   JDIMENSION *in_row_group_ctr,
                                   JDIMENSION in_row_groups_avail,
                                   _JSAMPARRAY output_buf,
                                   JDIMENSION *out_row_ctr,
                                   JDIMENSION out_rows_avail);
#endif


/*
 * Initialize for a processing pass.
 */

METHODDEF(void)
start_pass_dpost(j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
{
  my_post_ptr post = (my_post_ptr)cinfo->post;

  switch (pass_mode) {
  case JBUF_PASS_THRU:
#if BITS_IN_JSAMPLE != 16
    if (cinfo->quantize_colors) {
      /* Single-pass processing with color quantization. */
      post->pub._post_process_data = post_process_1pass;
      /* We could be doing buffered-image output before starting a 2-pass
       * color quantization; in that case, jinit_d_post_controller did not
       * allocate a strip buffer.  Use the virtual-array buffer as workspace.
       */
      if (post->buffer == NULL) {
        post->buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
          ((j_common_ptr)cinfo, post->whole_image,
           (JDIMENSION)0, post->strip_height, TRUE);
      }
    } else
#endif
    {
      /* For single-pass processing without color quantization,
       * I have no work to do; just call the upsampler directly.
       */
      post->pub._post_process_data = cinfo->upsample->_upsample;
    }
    break;
#if defined(QUANT_2PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16
  case JBUF_SAVE_AND_PASS:
    /* First pass of 2-pass quantization */
    if (post->whole_image == NULL)
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    post->pub._post_process_data = post_process_prepass;
    break;
  case JBUF_CRANK_DEST:
    /* Second pass of 2-pass quantization */
    if (post->whole_image == NULL)
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    post->pub._post_process_data = post_process_2pass;
    break;
#endif /* defined(QUANT_2PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16 */
  default:
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    break;
  }
  post->starting_row = post->next_row = 0;
}


/*
 * Process some data in the one-pass (strip buffer) case.
 * This is used for color precision reduction as well as one-pass quantization.
 */

#if BITS_IN_JSAMPLE != 16

METHODDEF(void)
post_process_1pass(j_decompress_ptr cinfo, _JSAMPIMAGE input_buf,
                   JDIMENSION *in_row_group_ctr,
                   JDIMENSION in_row_groups_avail, _JSAMPARRAY output_buf,
                   JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
{
  my_post_ptr post = (my_post_ptr)cinfo->post;
  JDIMENSION num_rows, max_rows;

  /* Fill the buffer, but not more than what we can dump out in one go. */
  /* Note we rely on the upsampler to detect bottom of image. */
  max_rows = out_rows_avail - *out_row_ctr;
  if (max_rows > post->strip_height)
    max_rows = post->strip_height;
  num_rows = 0;
  (*cinfo->upsample->_upsample) (cinfo, input_buf, in_row_group_ctr,
                                 in_row_groups_avail, post->buffer, &num_rows,
                                 max_rows);
  /* Quantize and emit data. */
  (*cinfo->cquantize->_color_quantize) (cinfo, post->buffer,
                                        output_buf + *out_row_ctr,
                                        (int)num_rows);
  *out_row_ctr += num_rows;
}

#endif


#if defined(QUANT_2PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16

/*
 * Process some data in the first pass of 2-pass quantization.
 */

METHODDEF(void)
post_process_prepass(j_decompress_ptr cinfo, _JSAMPIMAGE input_buf,
                     JDIMENSION *in_row_group_ctr,
                     JDIMENSION in_row_groups_avail, _JSAMPARRAY output_buf,
                     JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
{
  my_post_ptr post = (my_post_ptr)cinfo->post;
  JDIMENSION old_next_row, num_rows;

  /* Reposition virtual buffer if at start of strip. */
  if (post->next_row == 0) {
    post->buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
        ((j_common_ptr)cinfo, post->whole_image,
         post->starting_row, post->strip_height, TRUE);
  }

  /* Upsample some data (up to a strip height's worth). */
  old_next_row = post->next_row;
  (*cinfo->upsample->_upsample) (cinfo, input_buf, in_row_group_ctr,
                                 in_row_groups_avail, post->buffer,
                                 &post->next_row, post->strip_height);

  /* Allow quantizer to scan new data.  No data is emitted, */
  /* but we advance out_row_ctr so outer loop can tell when we're done. */
  if (post->next_row > old_next_row) {
    num_rows = post->next_row - old_next_row;
    (*cinfo->cquantize->_color_quantize) (cinfo, post->buffer + old_next_row,
                                          (_JSAMPARRAY)NULL, (int)num_rows);
    *out_row_ctr += num_rows;
  }

  /* Advance if we filled the strip. */
  if (post->next_row >= post->strip_height) {
    post->starting_row += post->strip_height;
    post->next_row = 0;
  }
}


/*
 * Process some data in the second pass of 2-pass quantization.
 */

METHODDEF(void)
post_process_2pass(j_decompress_ptr cinfo, _JSAMPIMAGE input_buf,
                   JDIMENSION *in_row_group_ctr,
                   JDIMENSION in_row_groups_avail, _JSAMPARRAY output_buf,
                   JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
{
  my_post_ptr post = (my_post_ptr)cinfo->post;
  JDIMENSION num_rows, max_rows;

  /* Reposition virtual buffer if at start of strip. */
  if (post->next_row == 0) {
    post->buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
        ((j_common_ptr)cinfo, post->whole_image,
         post->starting_row, post->strip_height, FALSE);
  }

  /* Determine number of rows to emit. */
  num_rows = post->strip_height - post->next_row; /* available in strip */
  max_rows = out_rows_avail - *out_row_ctr; /* available in output area */
  if (num_rows > max_rows)
    num_rows = max_rows;
  /* We have to check bottom of image here, can't depend on upsampler. */
  max_rows = cinfo->output_height - post->starting_row;
  if (num_rows > max_rows)
    num_rows = max_rows;

  /* Quantize and emit data. */
  (*cinfo->cquantize->_color_quantize) (cinfo, post->buffer + post->next_row,
                                        output_buf + *out_row_ctr,
                                        (int)num_rows);
  *out_row_ctr += num_rows;

  /* Advance if we filled the strip. */
  post->next_row += num_rows;
  if (post->next_row >= post->strip_height) {
    post->starting_row += post->strip_height;
    post->next_row = 0;
  }
}

#endif /* defined(QUANT_2PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16 */


/*
 * Initialize postprocessing controller.
 */

GLOBAL(void)
_jinit_d_post_controller(j_decompress_ptr cinfo, boolean need_full_buffer)
{
  my_post_ptr post;

#ifdef D_LOSSLESS_SUPPORTED
  if (cinfo->master->lossless) {
#if BITS_IN_JSAMPLE == 8
    if (cinfo->data_precision > BITS_IN_JSAMPLE || cinfo->data_precision < 2)
#else
    if (cinfo->data_precision > BITS_IN_JSAMPLE ||
        cinfo->data_precision < BITS_IN_JSAMPLE - 3)
#endif
      ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);
  } else
#endif
  {
    if (cinfo->data_precision != BITS_IN_JSAMPLE)
      ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);
  }

  post = (my_post_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
                                sizeof(my_post_controller));
  cinfo->post = (struct jpeg_d_post_controller *)post;
  post->pub.start_pass = start_pass_dpost;
  post->whole_image = NULL;     /* flag for no virtual arrays */
  post->buffer = NULL;          /* flag for no strip buffer */

  /* Create the quantization buffer, if needed */
  if (cinfo->quantize_colors) {
#if BITS_IN_JSAMPLE != 16
    /* The buffer strip height is max_v_samp_factor, which is typically
     * an efficient number of rows for upsampling to return.
     * (In the presence of output rescaling, we might want to be smarter?)
     */
    post->strip_height = (JDIMENSION)cinfo->max_v_samp_factor;
    if (need_full_buffer) {
      /* Two-pass color quantization: need full-image storage. */
      /* We round up the number of rows to a multiple of the strip height. */
#ifdef QUANT_2PASS_SUPPORTED
      post->whole_image = (*cinfo->mem->request_virt_sarray)
        ((j_common_ptr)cinfo, JPOOL_IMAGE, FALSE,
         cinfo->output_width * cinfo->out_color_components,
         (JDIMENSION)jround_up((long)cinfo->output_height,
                               (long)post->strip_height),
         post->strip_height);
#else
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
#endif /* QUANT_2PASS_SUPPORTED */
    } else {
      /* One-pass color quantization: just make a strip buffer. */
      post->buffer = (_JSAMPARRAY)(*cinfo->mem->alloc_sarray)
        ((j_common_ptr)cinfo, JPOOL_IMAGE,
         cinfo->output_width * cinfo->out_color_components,
         post->strip_height);
    }
#else
    ERREXIT(cinfo, JERR_NOTIMPL);
#endif
  }
}

#endif /* BITS_IN_JSAMPLE != 16 || defined(D_LOSSLESS_SUPPORTED) */

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Created: 2026-03-12 07:03